1. Field of the Invention
The disclosures discussed herein relate to an image forming apparatus and an image forming method.
2. Description of the Related Art
Image forming apparatuses employing an ink-jet system exhibit excellent apparatus downsizing and reduced-noise properties. The ink-jet system may be defined as a system to discharge ink (liquid droplets) onto a recording medium to form an image on a surface of the recording medium.
Japanese Laid-open Patent Publication No. 2004-330568 (hereinafter referred to as “Patent Document 1”) discloses a technology in an inkjet printer to coat a precoat liquid serving as a pretreatment liquid to form an ink-receiving layer on a continuous form sheet of paper, apply activation to aggregate pigments of pigmented ink to the continuous form sheet, and discharge the ink on a surface of the continuous form sheet to form images.
Such an inkjet printer generally employs a method of coating the transported continuous form sheet with the precoat liquid discharged by a spray, and drying the recording sheet by heating before and after the transported continuous form sheet is coated with the precoat liquid.
However, with this method, a recorded result appears to have low resistance to scuffing. That is, the pigmented ink is susceptible to easily coming off since the pigments of the pigmented ink are adhered to the surface of the recording medium. Hence, the inkjet printer further employs a method of coating the recorded images with a posttreatment liquid having a resin film, and the like to physically protect the recorded images in order to improve the resistance to scuffing.
However, in the inkjet printer, an optimal coating amount of the pretreatment liquid (i.e., the precoat liquid) may, for example, vary with printing conditions, and hence, the optimal coating amount of the pretreatment liquid may vary with the resolution of images to be recorded.
For example, in a case of recording low resolution images, ink dot diameters to be formed on the recording sheet tend to be large compared to a case of recording high resolution images. As a result, it may take a longer time to dry the ink due to the greater ratio of surface to ink volume for each of the dots. In addition, a recording velocity is higher in printing the low resolution images than the high resolution images, which may also result in taking a longer time to dry the ink. This indicates low permeability, which may cause ink spreading or ink beading.
Thus, a method for optimally controlling the coating amount of the pretreatment liquid has been desired in order to prevent ink spreading or ink beading.
Further, a longer coating time may be required for coating the recorded images with the posttreatment liquid, due to a large amount of the posttreatment liquid being required. Hence, there has been required a method of reducing the coating time.
Moreover, when the coating amount of the pretreatment liquid and the discharging amount of the posttreatment liquid are different, the following drawbacks may need to be dealt with after the drying process. That is, after the drying process, the recorded sheet may result insufficient dryness when the amounts of the pretreatment liquid and the posttreatment liquid are large, and the recorded sheet may shrink due to excessive dryness when the amounts of the pretreatment liquid and the posttreatment liquid are small.